This is the 648th most frequent Korean word.
수사에
"수사에" translates to "in the investigation" in English.
In this sentence, '수사에' links to the phrase '수사에 대한', referring to things related to the investigation.
수사에 대한 언론 보도가 끊이지 않았다.
The press reports about the investigation were non-stop.
'수사에' in this sentence modifies '필요한 자료', contextualizing the resources as being for the investigation.
경찰은 수사에 필요한 자료를 수집하고 있다.
The police are gathering materials necessary for the investigation.
Here, '수사에' functions as a part of the phrase '수사에 참여했습니다', indicating involvement in an investigation.